Effects of host's diet on two pupal parasitoids of the gypsy moth: Brachymeria intermedia (Nees) and Coccygomimus turionellae (L.).
In laboratory studies in Massachusetts with a synthetic diet and the foliage of 4 forest trees (grey birch (Betula populifolia), white oak (Quercus alba), red maple (Acer rubrum) and red oak (Q. rubra)), the weight of pupae of Lymantria dispar (L.) was significantly dependent on larval diet. The largest pupae were produced by the synthetic diet. Of the foliage diets, grey birch produced the largest pupae and white oak the smallest; these pupae varied in their suitability for 2 pupal parasites. For Brachymeria intermedia (Nees), the largest and heaviest parasites emerged from hosts reared on red oak, although parasite weight was not correlated with host weight. Female pupae from larvae reared on red oak were the most digestible of the host types, and males from the same source were most efficiently converted to parasite biomass. For Pimpla turionellae (L.) (Coccygomimus turionellae), parasite weight was correlated with host weight. Large hosts were most digestible for the parasites and were most efficiently converted to biomass. For both parasites, the percentage emergence was highest on hosts producing smaller parasites, and male hosts were utilised more efficiently than female hosts. In studies with Hyphantria cunea (Dru.) on the foliage of 4 trees, pupal weight also differed significantly with larval diet. Pin cherry (Prunus pensylvanica) produced the heaviest pupae, followed by black cherry (P. serotina), shagbark hickory (Carya ovata) and white ash (Fraxinus americana). The heaviest adults of Pimpla turionellae emerged from hosts from black cherry. It is suggested that intraspecific variability in hosts due to food-plant, and modified by host sex, may influence host suitability, a finding likely to be of importance for the biological control of polyphagous herbivores.